The 80s economic bubble, basically. It's always been less of a religious thing there, so it was easy to sell as a couples event to get rich young people spending.
Honestly the biggest revelation in this chapter is that Koga's father is actually around. I just kind of assumed that he was living with a single mother.
Somewhere down the line her ex will for sure come back, but I don't think there should be anymore rivals. They're rightfully happy, and the inner conflict when they learn the ins and outs of a relationship is plenty enough.